The Optical Coherence Tomography (OCT) is known for obtaining a tomogram of the structure under a skin by applying the light through a living body skin and detecting the reflected light from an internal anatomy) See Japanese Patent Application Laid-Open No. 2004-191114).
FIG. 11(A) shows a prior art an optical coherence tomography system. In FIG. 11(A), an optical coherence tomography system 8 includes a low coherence light source 81, a condensing lens 82, a half-mirror 83, a reference mirror 84, an actuator for moving the reference mirror 85, an object lens 86, a detecting lens 87, a light detector 88 and a control computer 89.
The elements of the optical coherence tomography system 8 excepting the low coherence light source 81 and the computer 89 constitutes an optical interferometer. A light source with a wide spectrum width like LED, SLD (Super Luminescent Diode), etc. is used as the low coherence light source 81 and has a spread wave length spectrum (e.g. tens nm or wider) as shown in FIG. 11(B).
The low coherence light source 81 is controlled by a control signal A1 from the computer 89. The light from the low coherence light source 81 is collimated by the condensing lens 82 and is output to the half mirror 83. The half-mirror 83 splits the light from the condensing lens 82 into two parts, directs one part to the reference mirror 84 and directs the other part to a measured object O through the object lens 86.
The half-mirror 83 also combines the reflected light from the reference mirror 84 with the reflected light from a reflection point within the measured object O and outputs the combined light to the light detector 88 through the detecting lens 87.
The reflected light from the measured object O includes the light reflected at the surface, the light reflected at a shallow internal point and the light reflected at a deep internal point.
Since the light uses for detection is a low coherence light, the reflected light which experienced an interference includes only the reflected light from the plane at the position where the distance form the half-mirror 83 is (L0±L0′/2), where L0 is the distance between the half-mirror 83 and the reference 84 and L0′ is the coherence length.
By changing the distance between the half-mirror 83 and the reference 84 by the actuator 85 (controlled by a control signal A2 from the computer 89) it is possible to selectively detect only the reflected light from the reflection plane that corresponds to the distance.
By this technique it is possible to calculate the reflection index at any position inside the measured object O by the computer 89 and provide the visual internal structure information for the measured object O by displaying the distribution of the calculated reflection index onto a display screen (not shown).